The invention relates generally to polymerization catalysts and, more specifically, to catalysts with high activity for atom transfer radical polymerization.
Atom transfer radical polymerization (ATRP) is a known “living” polymerization technique used to polymerize vinyl monomers for the preparation of polymers and copolymers with predictable molecular weight and well-defined architecture. (Wang, J. S.; Matyjaszewski, K. J. Am. Chem. Soc. 1995, 117, 5614; Patten, T. E.; Matyjaszewski, K. Acc. Chem. Res. 1999, 32, 895; Matyjaszewski, K.; Xia, J. Chem. Rev. 2001, 101, 2921.) However, a high concentration (2000˜10,000 ppm relative to monomer) of transition-metal catalysts makes them precipitate with and hence contaminate the polymer product. Thus, the technical challenge for ATRP is how to reduce the residual catalyst in the product. (Matyjaszewski, K.; Xia, J. Chem. Rev. 2001, 101, 2921; Shen, Y; Tang, H; Ding, S. Prog. Polym. Sci. 2004, 29, 1053.) One approach is to remove the catalyst by post-purification, such as washing, reprecipitation (Kasko, A. M.; Heintz, A. M.; Pugh, C. Macromolecules 1998, 31, 256) and adsorption (Matyjaszewski, K.; Pintauer, T.; Gaynor, S. Macromolecules 2000, 33, 1476), which has been demonstrated on a bench scale. However, these methods lead to high cost, loss of polymer, and scale-up difficulties.
Another approach is to use liquid-liquid biphasic (Xia, J.; Johnson, T.; Gaynor, S. G.; Matyjaszewski, K.; DeSimone, J. Macromolecules 1999, 32, 4802-4805; Carmichael, A. J.; Haddleton, D. M.; Bon, S. A. F.; Seddon, K. R. Chem. Commun. 2000, 1237-1238; Sarbu, T.; Matyjaszewski, K. Macromol. Chem. Phys. 2001, 202, 3379-3391; Haddleton, D. M.; Jackson, S. G.; Bon, S. A. F. J. Am. Chem. Soc. 2000, 122, 1542-1543; Ding, S.; Radosz, M.; Shen, Y. Macromolecules 2005, 38, 5921-5928) and solid-supported catalysts. (Kickelbick, G.; Paik, H.-j; Matyjaszewski, K. Macromolecules 1999, 32, 2941-2947; Haddleton, D. M.; Kukulj, D.; Radigue, A. P. Chem. Commun. 1999, 99; Shen, Y.; Zhu, S.; Zeng, F.; Pelton, R. J. Polym. Sci. Part A: Polym. Chem. 2001, 39, 1051-1059; Shen, Y.; Zhu, S.; Pelton, R. Macromolecules 2001, 34, 5812-5818; Hong, S. C.; Matyjaszewski, K. Macromolecules 2002, 35, 7592-7605; Hong, S. C.; Neugebauer, D.; Inoue, Y.; Lutz, J. F.; Matyjaszewski, K. Macromolecules 2003, 36, 27-35; Honigfort, M. E.; Brittain, W. J. Macromolecules 2003, 36, 3111-3114; Nguyen, J. V.; Jones, C. W. Macromolecules 2004, 37, 1190-1203; Nguyen, J. V:; Jones, C. W. J. Cata. 2005, 232, 276-294) However, these methods lead to lower degree of polymerization control and higher cost. (Shen et al., 2004).
An alternative approach to reducing the catalyst residue in the ATRP product is to increase the catalyst activity and hence decrease its concentration to the point where the catalyst can economically be left in the polymer product, an approach which is common to polyolefin technology. (Hlatky, G. G. Chem. Rev. 2000, 100, 1347-1376) Matyjaszewski et al. first reported examples of such highly active catalysts, first CuBr/Me6TREN and later CuBr/Me4TAPH. (Xia, J. and Matyjaszewski, K. Macromolecules 1998, 31, 5958; Inoue, Y.; Matyjaszewski, K. Macromolecules 2004, 37, 4014-4021) A 10 mol % CuBr/Me6TREN relative to the initiator (Cu/initiator molar ratio Cu/I=0.1) was sufficient to polymerize methyl acrylate (MA) and yielded polymer with low polydispersity. Well-controlled poly(butyl acrylate) was prepared at 5 mol % CuBr/Me4TAPH relative to the initiator. For styrene (St) polymerization, 50 mol % catalyst (Cu/I=0.5) relative to the initiator worked well, but 10 mol % catalyst relative to the initiator resulted in low monomer conversion (20%) and high polymer polydispersity (PDI>1.5). This catalyst did not work for methyl methacrylate (MMA).
Along the same lines, Guan and Smart found that UV irritation substantially increased the catalytic activity of CuCl/bipyridine for MMA polymerization. At 2.1% CuCl/bipyridine relative to the initiator (Cu/I=0.021), 75% MMA conversion was obtained in 16 h. (Guan, Z.; Smart, B. Macromolecules 2000, 33, 6904-6906.) More recently, Faucher and Zhu reported that, with 1 mol % catalyst relative to initiator, a heterogeneous catalyst CuBr/HMTETA polymerized MMA at 90° C. to about 50% conversion with PDI of 1.1. At lower catalyst concentration (0.1 mol % vs the initiator), the polymerization control was lost (PDI=6.3). (Faucher, S.; Zhu, S. Ind. Eng. Chem. Res. 2005, 44, 677.)